This invention relates broadly to an apparatus and method for applying a thermoplastic bead in a circular pattern. In one aspect the invention relates to method and apparatus for applying liquid adhesives, particularly hot melted adhesives.
In many operations, it is desirable to apply a bead of a thermoplastic adhesive to a substrate to bond materials to the substrate. Examples of such uses are disclosed in U.S. Pat. No. 4,798,163 which relates to a slit nozzle for application of hot melt adhesives. U.S. Pat. No. 4,711,683 discloses method and apparatus for applying elastic bands or ribbons to a thermoplastic web.
The patterns of the bead applied may range from a wide ribbon as disclosed in U.S. Pat. No. 4,798,163 to a zig-zag pattern as disclosed in U.S. Pat. No. 4,711,683.
In some applications it is also desirable to apply the bead in a circular or oval pattern to effect uniform distribution of the polymer onto the substrate. Applicators constructed in accordance with U.S. Pat. No. 3,634,573 may be adapted to apply a circular bead on the substrate. This design operates on the principle of a single thermoplastic adhesive filament being extruded through a nozzle while a plurality of hot air streams are angularly directed onto the extruded filament to impart a circular motion thereto. The filament thus assumes an expanding swirling cone shaped pattern in moving from the extrusion nozzle to the substrate. As the substrate is moved linearly with respect to the stationary nozzle, a circular bead is continuously deposited on the substrate, each circular cycle being displaced from the previous cycle by a small amount in the direction of substrate movement.
As indicated above, the swirling, expanding circular pattern is achieved by gas streams impinging upon the extruded polymer. References which disclose apparatus for applying a plurality of gas streams to extruded thermoplastic or glass materials include U.S. Pat. No. 3,634,573, U.S. Pat. No. 4,135,903, U.S. Pat. No. 4,243,400, U.S. Pat. No. 4,211,736, and U.S. Pat. No. 4,548,632.
U.S. Pat. No. 4,891,249, disclosed a spray nozzle for generating fibers or filaments. These generated fibers and filaments are not swirled. For reasons described in detail below, the generation of the filament and swirls offer significant advantages.